An internal combustion engine is provided with a number of cylinders, each of which is connected to an intake manifold by means of at least one intake valve and to an exhaust manifold by means of at least one exhaust valve. The intake manifold receives fresh air (i.e. air from the external environment) through a feeding pipe provided with a butterfly valve and is connected to the cylinders by means of corresponding intake pipes, each of which ends at least one intake valve.
In modern internal combustion engines, the intake manifold is more and more frequently of the variable geometry type, i.e. is provided with a choke device, which varies the introduction section of the air in the intake pipes according to the engine speed (i.e. to the angular speed of rotation of the crankshaft) to increase the engine performances by reducing at the same time the polluting emissions. At low speeds, the introduction section of the air through the intake pipes is decreased so as to generate turbulences in the intake air flow which improve the mixing of air and fuel in the cylinders; in virtue of the presence of these turbulences which improve the mixing all the injected fuel is burnt and therefore the polluting emissions generated by the combustion are reduced. At high speeds, the introduction section of the air is maximised through the intake pipes so as to allow a complete filling of the cylinders and therefore allow the generation of the maximum possible power.
For example, the choke devices of the type described above may be either tumble devices or swirl devices. For each intake pipe, a tumble device uses a choke body mobile between an active (or choke) position, in which the choke body reduces the transversal section of the intake pipe, and a home (or maximum opening) position, in which the choke body does not determine any reduction of the air introduction section of the intake pipe. For each intake pipe, a swirl system contemplates that each intake pipe comprises two channels and uses a choke body inserted in one of the two channels and mobile between the active position, in which the choke body completely closes the corresponding channel, and a home position (or maximum opening position), in which the choke body does not determine a significant reduction of the introduction section of the air of the corresponding channel.
In the commercial choke devices, all the choke bodies are keyed onto a common shaft to turn together from and towards the active position under the bias of a common actuator device, which is adapted to simultaneously and synchronously control the position of all the choke devices themselves. Normally, the common actuator device integrates therein a pair of mechanical stoppers, which respectively determine the location of the active position and of the home position; the function of the mechanical stoppers is both to delimit the range of displacement of the choke bodies, and to constitute a positive position reference for the driving system of the actuator device.
It has been observed that due to the constructive tolerances of the commercial choke devices, the actual location of the active and home positions determined by the mechanical stoppers integrated in the common actuator device may present a considerably difference with respect to the ideal location hypothesised in design. A first solution to this problem was to reduce the constructive tolerances by using more precise machining processes; however, such solution implies an inevitable and considerable increase in production costs.